322 



PART 1IT. THE CLASSIFICATION OF PLANTS. 



other allied Lichens litmus is prepared : Eamalina and Evernia, with a ribbon 

 shaped flattened thallus, occur on trees and wooden fences : Cetraria islandica 

 is the Iceland Moss, which forms a mucilaginous fluid when boiled with water : 

 Anaptychia ciliaris, which resembles the foliaceous Lichens, with a flattened 

 thallus, is common on the trunks of trees : Cladonia has a scaly decumbent 

 thallus, from which erect branches spring bearing the apothecia; Cladonia 

 fimbriata is common; Cladonia rangiferina, the Eeindeer Moss, occurs on 

 moors : Sphasrophorus has the same external appearance, but it is pyreno- 

 carpous. 



(b) foliaceous Lichens, in which the thallus is flattened and adheres to the 

 substratum : the green (rarely bluish-green) algal cells form a single layer 

 beneath the upper surface (Fig. 229). The margin of the thallus is usually 

 lobed. 



Parmelia parietina occurs, with its bright yellow thallus bearing apothecia, 



, . , on tree-trunks and walls, to- 

 gether with other species of 

 a grey colour ; Sticta pulmon- 

 acea (Fig. 230 B) has a reti- 

 culated yellowish thallus, and 

 grows on tree-trunks : Pelti- 

 gera is represented by several 

 species which grow on mossy 

 banks in woods; the apothecia 

 are borne on the margin of 

 the lobes of the thallus : Um- 

 bilicaria and Gyrophora, of a 

 dark colour, grow on silicious 

 rocks : Endocarpon has a 

 grey thallus with numerous 

 small peri thecia, which appear 

 as black dots ; it grows on 

 rocks. 



(c) crustaceans Lichens, in 

 which the thallus is usually 

 indefinite in outline, and can 

 of ten be scarcely distinguished 

 from the substratum, the 

 fructification alone being con- 

 spicuous. 



The Lichens of this form 

 are extremely numerous. 

 Among them may be men- 

 tioned the Lecanorese, of 

 which Lecanora subfusca occurs on the trunks of trees : the Lecideace, which 

 occur mainly on earth and rocks, Lecidea geographica, forming bright yellow 

 incrustations of considerable extent on silicious rocks : the Graphidese, of which 

 Graphis scripta is common on the trunks of Beeches and other trees : the 

 small Calicieas, which are common on wooden fences : the Bseomycere, of which 



FIG. 229. Transverse section of the heteromerous 

 thallus of Sticta fuliginosa (x 600). o Cortex of the 

 upper surface ; u under surface ; m network of 

 hyphae forming the medullary layer; g algal cells; 

 v root-like outgrowths (rhizines) of the under surface. 

 (After Sachs.) 



